1. Field of the Invention
The present invention relates to a normal mode adjustment position detection method and adjustment method for a bar-shaped or annular vibration driven motor or actuator.
2. Related Background Art
FIG. 7 is an exploded perspective view of a vibrating member of a bar-shaped vibration driven motor, and FIG. 8 is a longitudinal sectional view of the bar-shaped vibration driven motor.
In a conventional vibrating member, a driving A-phase piezoelectric element al including a group of two piezoelectric element plates PZT1 and PZT2, a driving B-phase piezoelectric element a2 including a group of two piezoelectric element plates PZT3 and PZT4, and a sensor piezoelectric element s1 including a piezoelectric element plate are stacked, as shown in FIG. 7. Electrode plates A1 and A2 for supplying power to the piezoelectric elements, and a sensor signal output electrode plate S are sandwiched between respective adjacent piezoelectric elements. In addition, GND electrode plates G1, G2, and G3 are arranged for giving a GND potential. Metal blocks b1 and b2 formed of, e.g., brass or stainless steel, which causes relatively small vibration attenuation, are arranged to clamp these piezoelectric element plates and electrode plates. The metal blocks b1 and b2 are fastened by a fastening bolt c to obtain an integrated structure, thereby applying a compression stress to the piezoelectric element plates. In this vibrating member, since an insulating sheet d is inserted between the bolt c and the metal block b2, only one sensor piezoelectric element s1 need be used.
The A- and B-phase piezoelectric elements a1 and a2 have an angular displacement of 90.degree. therebetween. These piezoelectric elements a1 and a2 respectively excite bending vibrations in directions within two orthogonal planes including the axis of the vibrating member, and have a proper temporal phase difference therebetween. Thus, surface portions of the vibrating member are caused to form a circular or elliptic motion, thereby frictionally driving a moving member pressed against the upper portion of the vibrating member.
FIG. 8 shows an example wherein such a vibrating member is used in a bar-shaped vibration driven motor. In this example, the fastening bolt c of the vibrating member has a small-diameter column portion c2 at its distal end portion. A fixing member g fixed to the distal end portion of the column portion c2 can fix the motor itself, and can also rotatably support, e.g., a rotor r. The rotor r contacts the front end face of the front metal block b1, and a pressure is given by pressing a coil spring h in a spring case i inserted in the rotor r through a bearing member e and a gear f.
In order to obtain high efficiency, both a bar-shaped vibration driven motors and annular vibration driven motor are designed, so that the natural frequencies of normal modes of two phases excited in the vibrating member coincide with each other.
However, in practice, each of these natural frequencies is shifted relative to the other due to variations in the material of the metal blocks constituting the vibrating member, pressure variations in the portions for clamping the PZT elements, and the like. Thus, when the two phases are driven at the same frequency, the amplitudes generated by the two phases have a difference therebetween, and a circular motion formed at the mass point of the vibrating member is distorted, resulting in a decrease in motor efficiency.